1. Field of the Invention
This invention relates to an alkali- and heat-resistant inorganic fiber and, more particularly, to alkali- and heat-resistant inorganic fibers, in which the fiberizing temperature is approximately the same as those of customary rock fibers.
2. Description of the Prior Art
Heretofore, some of glass fibers have been known as alkali-resistant inorganic fibers. These glass fibers, however, show a high viscosity in the molten state such as, for example, 100 poises at 1,400.degree. C. Owing to such high viscosity, one is unable to manufacture short fibers by a multirotor spinning process, which operates only under low melt viscosity conditions as in the case of rock fibers with a viscosity of several poises at 1,400.degree. C. Moreover, there are other disadvantages for producing the alkali-resistant glass fibers. It is necessary to add zirconium oxide, which is expensive and, furthermore gives rise to an increased melting cost.
There has recently been disclosed alkali-resistant rock fibers which dispense with expensive zirconium oxide used in conventional alkali-resistant glass fibers U.S. Pat. No. 4,205,992, [Japanese Patent Application "Kokai" (Laid-open), No. 101,922/1979]. The disclosed fibers, however, have considerably high fiberizing temperature, comparing with those of customary rock fibers. This causes a remarkable increase in energy cost for manufacturing fibers of optimal diameter by means of a multirotor.